1. Field of the Invention
This invention relates to an improved peripheral seal for use in liquid storage tanks wherein the tank sidewalls are welded, riveted, or bolted, and are cylindrically shaped.
2. Description of Prior Art
Petroleum products and hydrocarbon liquids, in general, are commonly stored above ground in large cylindrical storage tanks. Those having vapor pressures less than one atmosphere are usually stored in tanks having fixed roofs or floating roofs which rise and fall with the liquid. Since the products stored are often volatile, it is, in such cases, necessary to prevent loss of the vapors which come off the liquid, to minimize losses and to prevent contamination of the atmosphere. An improved method of vapor loss control is a floating cover which closes off the surface of the stored product, thus preventing evaporation. A floating roof fulfills this requirement. For fixed roof tanks, it is common practice to install a floating cover inside the tank to perform that function. These floating covers and roofs, are, in themselves impermeable to the vapors contained. Being made normally of metal or plastic and being rigid in nature, it is necessary to leave an annular space around the floating device (floater) to prevent interference between it and the tank wall in case of irregularity of shape in either member. It is then necessary to close up the annular space with a flexible seal which is connected and sealed to the floater and which pushes sealingly against the tank wall as the floater rises and falls.
To date, a number of designs of such seals have been employed, all of which suffer to some extent in their ability to provide a positive seal under all the conditions encountered in the field. For instance, the following prior art patents all disclose varying seal structures for use in vertical storage tanks:
U.s. pat. Nos. PA0 3,595,432--Ven der Heijden et al. PA0 3,059,805--Joor PA0 2,987,215--Joor PA0 2,784,863--Fabian PA0 2,459,178--Moyer PA0 2,313,856--Wiggins PA0 2,148,811--Griffin PA0 2,082,194--Wiggins PA0 1,979,657--Wiggins
Basically the prior art discloses a series of formed metal shoes arranged end to end around the periphery of the floater that are pressed flat against the tank wall by means of connecting arms with springs or weights, all of these elements being connected to the floater. The space between the upper edge of the sealing plates and the outer rim of the floater is closed up with a strip of fabric connected to the floater rim and to the upper edges of the plates.
Also, other sealing devices are known wherein the annular space is closed by placing into it a fabric tube somewhat larger in diameter than the width of the space, with the tube being filled either with liquid or with resilient foam to provide the sealing pressure against the tank wall. The fabric tubing is, of course, connected to the outer rim of the floater.
Both types of seals work well in tanks with relatively smooth, regular, walls. However, in lap welded tanks or bolted or riveted tanks, the sealing effect is adversely affected and the protrusions cause excessive wear. Further, the protrusions cause the formation of openings between the seal and the tank wall which often places the system in an unacceptable category insofar as the Environmental Protection Agency is concerned.
Accordingly, it is an object of the present invention to provide an improved peripheral seal useful for sealing liquid storage tanks having cylindrical walls, sometimes irregularly shaped and with randomly occurring protrusions such as rivets, bolts, or lap-welded seams.